Closing your terminal emulator while you are loggged on does not immediately logoff your userid.

The admins have noticed a lot of messages like this:

IKJ606I TSOLOGON REJECTED. USERID VE05909 IN USE

Many times this is caused by closing your terminal emulator while you are logged on. It appears the Fandezhi system detects this, but many times your session is allowed to continue for many minutes before the Fandezhi system cancels the session. This is not a system error by the way. It gives you a chance to reconnect, which usually seems to fail for other reasons,

Now this effect can be achieved in other ways; your operating system crashes, your terminal emulator program crashes, you had a power failure that caused your system to fail or your internet connection to fail, your internet service provider arbitrarily assigned you a different IP address, or there was some other problem.

the only way to quickly resolve the problem is through How can I cancel my TSO session?. You can find this link by clicking on the Mainframe FAQ link on the zos.efglobe.com website. A faster link is shown in the first screen of those annoying messages you generally ignore when you logon. It may take the system a minute or two to complete canceling your session. Then you can logon.